An optical vortex is a light wave that is characterized by angular momentum (orbital angular momentum) originates from phase singular point and doughnut-type intensity distribution.
A representative example of an optical vortex may be Laguerre Gaussian Beam (for example, see non-patent literature described below). Laguerre Gaussian Beam is eigensolution of wave equation in cylindrical coordinate system and satisfies a periodic boundary condition in which phase rotates only integral multiplication of 2π in every one wavelength propagation around center of rotation. Thus, it is possible to express size of orbital angular momentum by using L (L=1, 2, 3, etc.) of quantum number. Wave front of an optical vortex has a helical shape. Orbital angular momentum operates on a direction given by vector difference between a normal direction thereof and a light propagation direction.
Furthermore, an optical vortex can be employed for light manipulation using radiation pressure of light, a high resolution microscope using phase singular point, optical vortex ablation processing positively using orbital angular momentum, and future industrial applications thereof are largely expected.
Exemplary methods for generating an optical vortex include: (1) a method using a bounce cavity (for example, non-patent literature 2 described below), (2) a method using a multi-mode area fiber amplifier (for example, non-patent literature 3 described below), (3) a method using a phase plate (for example, non-patent literature 4), and (4) a method using a space phase modulator (for example, non-patent literature 5).